This invention relates to methods and apparatus for processing photographic film strips and more particularly, it concerns an improved method and apparatus by which processing fluid supplied in the processor of a multipurpose film cassette is distributed uniformly over the surface of a strip of exposed film under conditions in which the hydrodynamic force developed by the nozzle and processing fluid is essentially equal to the spring force retaining the film strip against the nozzle.
As a result of recent developments in the motion picture art, a system has been devised by which a supply of light sensitive film contained in a multipurpose cassette can be exposed in a camera adapted to receive the cassette and then processed or developed to provide the conventional series of positive transparent image frames merely by placing the cassette in a viewing apparatus capable of activating a processor also contained in the cassette such that upon rewinding the exposed film, a coating or layer of processing fluid is deposited along the length of the film. After processing in this manner, the viewing device is operated as a projector to advance the film incrementally, frame by frame, past a light source so that the scene to which the film was exposed is reproduced on a screen. Preferably, the processing fluid effects a diffusion transfer of a negative image in a light sensitive emulsion layer to a positive image receiving layer.
While the advance in the motion picture art represented by such a system is apparent and needs no elaboration herein, it is to be noted as critical to satisfactory operation of the system that the processing fluid must be deposited uniformly within extremely small tolerances over the emulsion layer on the film during processing. Failure to achieve such uniform layer of the developing or processing fluid on the film strip emulsion will result in undesirable blemishes such as streaks, spots or the like in the image viewed during projection of the processed film.
The problems of achieving a uniform layer or coating of the fluid on the film during the processing operation can be readily understood by taking cognizance of the basic system requirement that each cassette carry its own processor and that the cassette and its components including the processor must be capable of mass production manufacturing techniques and the tolerance level incident to such techniques for the system as a whole to be acceptable in a competitive commercial market. Heretofore, a most promising solution to the problems involved the use of a molded nozzle structure provided with an inclined doctoring surface downstream from an opening through which the processing fluid passes into contact with the film strip during rewinding travel after exposure. The inclined doctoring surface of the nozzle provided a positive pressure gradient increasing in the direction of film travel to achieve uniform distribution of the deposited processing fluid. A processor of this type is disclosed in a copending application Ser. No. 360,678 filed May 16, 1973 by Edward F. Burke, Jr. et al, now issued on Mar. 11, 1975 as U.S. Pat. No. 3,871,013 and assigned to the assignee of the present invention.
Although the use of an inclined doctoring surface by which the processing fluid is distributed under a pressure gradient over the exposed emulsion of the film strip has proven to be a reasonable solution to the problems of achieving the necessary uniform deposition of processing fluid, other problems have been experienced with the accumulation of macroscopic or smaller particles at the trailing edge of the doctoring blade last to contact the processing fluid as it is deposited. Such particles are believed to be as a result of dust on the film which may enter the cassette through vent passages either during cassette storage prior to exposure or during exposure of the film while the cassette is loaded in a camera. The effect of the particles on the doctoring blade is the development of undesirable linear irregularities or streaking in the processing fluid layer deposited on the film. Such linear irregularities or streaks are often visible as blemishes in the image viewed during projection of the film strip. Further it has been noted that such streaking progresses in severity toward the end of the film strip which is last to pass under the nozzle and receive the deposition of processing fluid during the rewind processing cycle thus suggesting an accumulation or build-up of particles on the doctoring blade as the processing operation progresses from one end to the other end of the film strip.